This invention relates to an apparatus for analyzing the carbon dioxide content of liquids and in particular, an apparatus for measuring the carbon dioxide content of carbonated soda water beverages.
In a sealed container such as a can or a bottle, a carbonated liquid beverage comes to equilibrium with the gas phase above the liquid and the equilibrium pressure is directly related to the carbon dioxide content of the liquid. The exact mathematical relationship between the carbon dioxide content of the liquid and the temperature and pressure of the container and its contents depends upon the acidity and other chemical properties of the beverage. These relationships have been determined empirically and carbon dioxide content of a beverage can be determined by measuring the pressure in the container. However, in a typical high speed bottling or canning line which run at hundreds of cans a minute, a procedure in which a container is removed and then gas pressure is measured would allow many containers to be filled before an adjustment could be made for the carbonation level of the beverage. There is a need to rapidly measure the beverage before it is bottled or canned so that adjustments to the carbonation level can be made if necessary.
The carbonated beverage can be analyzed by removing a sample from the filling line and placing the beverage sample in a sealed container and allowing the beverage to come to equilibrium with the carbon dioxide gas. This usually requires several hours.
Prior techniques have been used to analyze samples such as shown in U.S. Pat. No. 3,077,765 issued Feb. 19, 1963 to Dijkema in which a sample of a beverage is removed and placed in a sealed container and the container is vibrated to bring the beverage into equilibrium with the carbon dioxide gas and the temperature of the beverage and gas and the pressure of the gas were determined. However, this method proved too slow and inaccurate since the amount of vibration needed to bring the gas and liquid to a state of equilibrium could not be accurately determined and changed with different beverages.
In U.S. Pat. No. 4,083,225 issued April 11, 1978 to Day et al, an ultrasonic transducer was placed in a beverage line and measured the quantity of gas bubbles in the beverage and determined carbon dioxide content from this measurement. This method also was inaccurate.
In U.S. Pat. Nos. 4,550,590 issued Nov. 5, l985 and 4,461,165 issued July 24, 1984 both to Kesson show a method and apparatus for measuring and monitoring the gas in a liquid by placing a semipermeable membrane across the face of a chamber containing liquid. Gas from the liquid permeates through the membrane into a chamber and the pressure within the chamber is measured. U.S. Pat. No. 4,179,918 issued Dec. 25,1979 to van Strien shows a method of measuring the carbon dioxide content of beer by placing beer in a vessel and electrically measuring the pressure of the carbon dioxide atmosphere above the beer.
None of these prior art methods provide a rapid and accurate method for continuously monitoring the carbon dioxide content of beverages such as carbonated soft drinks.